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CONTENTS
Volume 20, Number 6, June 2015
 

Abstract
Full scale measurement on the structural dynamic characteristics and Vortex-induced Vibrations (VIV) of a long-span suspension bridge with a central span of 1650 m were conducted. Different Finite Element (FE) modeling principles for the separated twin-box girder were compared and evaluated with the field vibration test results, and the double-spine model was determined to be the best simulation model, but certain modification still needs to be made which will affect the basic modeling parameters and the dynamic response prediction values of corresponding wind tunnel tests. Based on the FE modal analysis results, small-scaled and large-scaled sectional model tests were both carried out to investigate the VIV responses, and probable Reynolds Number effects or scale effect on VIV responses were presented. Based on the observed VIV modes in the field measurement, the VIV results obtained from sectional model tests were converted into those of the three-dimensional (3D) full-scale bridge and subsequently compared with field measurement results. It is indicated that the large-scaled sectional model test can probably provide a reasonable and effective prediction on VIV response.

Key Words
twin-box girder suspension bridge; dynamic characteristics; VIV response; FE modeling; sectional model test; field measurement; Reynolds Number effects

Address
Yongxin Yang and Yaojun Ge: State Key Lab for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
Tingting Ma: College of Ocean Science and Engineering, Shanghai Maritime University, Shanghai 201306, China

Abstract
Field measurement of wind characteristics is of great significance for the wind engineering community. High-frequency anemometers such as ultrasonic anemometers are widely used to obtain the high-frequency fluctuating wind speed time history. However, conventional instrumentation systems may suffer from low efficiency, non-real time transmission and higher maintenance cost, and thus are not very appropriate in the field measurement of strong winds in remote areas such as mountain valleys. In order to improve the field measurement performance in those remote areas, a wireless high-frequency anemometer instrumentation system for field measurement has been developed. In this paper, the architecture of the proposed instrumentation system, and measured data transmission and treatment will be presented firstly. Then a comparison among existing instrumentation systems and the proposed one is made. It shows that the newly-developed system has considerable advantages. Furthermore, the application of this system to the bridge site located in the mountain valley is discussed. Finally, typical samples of measured data from this area are presented. It can be expected that the proposed system has a great application potential in the wind field measurement for remote areas such as the mountainous or island or coastal area, and hazardous structures such as ultra-voltage transmission tower, due to its real-time transmission, low cost and no manual collection of data and convenience.

Key Words
field measurement; high-frequency anemometers; data wireless transmission; General Packet Radio Service (GPRS) network; cloud server; mountain area

Address
Guoqing Huang, Liuliu Peng, Yanwen Su, Haili Liao and Mingshui Li: Research Center for Wind Engineering, School of Civil Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, China

Abstract
A multi-platform offshore wind farm is receiving the worldwide attention for the sake of maximizing the wind power capacity and the dynamic stability at sea. But, its wind power efficiency is inherently affected by the interference of wake disturbed by the rotating blades, so its layout should be appropriately designed to minimize such wake interference. In this context, the purpose of this paper is to introduce a layout optimization for multi-platform offshore wind farm consisted of 2.5MW spar-type floating wind turbines. The layout is characterized by the arrangement type of wind turbines, the spacing between wind turbines and the orientation of wind farm to the wind direction, but the current study is concerned with the spacing for a square-type wind farm oriented with the specific angle. The design variable and the objective function are defined by the platform length and the total material volume of the wind farm. The maximum torque loss and overlapping section area are taken as the constraints, and their meta-models expressed in terms of the design variable are approximated using the existing experimental data and the geometry interpretation of wake flow.

Key Words
layout optimization; multi-platform offshore wind farm; wind turbine spacing; torque loss; overlapping section area; response surface method (RSM)

Address
E.H. Choi, J.R. Cho and O.K. Lim: School of Mechanical Engineering, Pusan National University, Busan 609-735, Korea

Abstract
\"Wind and Ports\" is a European project that has been carried out since 2009 to handle wind forecast in port areas through an integrated system made up of an extensive in-situ wind monitoring network, the numerical simulation of wind fields, the statistical analysis of wind climate, and algorithms for medium-term (1-3 days) and short term (0.5-2 hours) wind forecasting. The in-situ wind monitoring network, currently made up of 22 ultrasonic anemometers, provides a unique opportunity for detecting high resolution thunderstorm records and studying their dominant characteristics relevant to wind engineering with special concern for wind actions on structures. In such a framework, the wind velocity of thunderstorms is firstly decomposed into the sum of a slowly-varying mean part plus a residual fluctuation dealt with as a non-stationary random process. The fluctuation, in turn, is expressed as the product of its slowly-varying standard deviation by a reduced turbulence component dealt with as a rapidly-varying stationary Gaussian random process with zero mean and unit standard deviation. The extraction of the mean part of the wind velocity is carried out through a moving average filter, and the effect of the moving average period on the statistical properties of the decomposed signals is evaluated. Among other aspects, special attention is given to the thunderstorm duration, the turbulence intensity, the power spectral density and the integral length scale. Some noteworthy wind velocity ratios that play a crucial role in the thunderstorm loading and response of structures are also analyzed.

Key Words
gust factor; monitoring network; moving average period; synoptic event; thunderstorm; turbulence; wind velocity

Address
Giovanni Solari, Massimiliano Burlando, Patrizia De Gaetano
and Maria Pia Repetto: Department of Civil, Chemical and Environmental Engineering (DICCA), University of Genoa, Via Montallegro, 1, 16145 Genoa, Italy

Abstract
Tests were conducted at the Florida International University (FIU) Wall of Wind (WOW) to investigate the susceptibility of Variable Message Signs (VMS) to wind induced vibrations due to vortex shedding and galloping instability. Large scale VMS models were tested in turbulence representative of the high frequency end of the spectrum in a simulated suburban atmospheric boundary layer. Data was measured for the 0 and 45 horizontal wind approach directions and vertical attack angles ranging from -4.5 to +4.5. Analysis of the power spectrum of the fluctuating lift indicated that vertical vortex oscillations could be significant for VMS with a large depth ratio attached to a structure with a low natural frequency. Analysis of the galloping test data indicated that VMS with large depth ratios, greater than about 0.5, and low natural frequency could also be subject to galloping instability.

Key Words
aerodynamic drag; galloping; variable message sign; vortex shedding

Address
Debbie Meyer, Arindam Gan Chowdhuryand Peter Irwin: Department of Civil and Environmental Engineering, Florida International University, Miami, FL, USA

Abstract
This study presents experimental and numerical aerodynamic investigation of a prototype vehicle. Aerodynamics forces examined which exerted on a prototype. This experimental study was implemented in a wind tunnel for the Reynolds number between 105-3.1x105. Numerical aerodynamic analysis of the vehicle is conducted for different Reynolds number by using FLUENT CFD software, with the k-e realizable turbulence model. The studied model aims at verifying the aerodynamic forces between experimental and numerical results. After the Reynolds number of 2.8x105, the drag coefficient obtained experimentally becomes independent of Reynolds number and has a value of 0.25.

Key Words
vehicle aerodynamic performance; CFD (computational fluid dynamics); design codes and standards; drag coefficient; pressure distribution

Address
Selahaddin Orhan Akansu, Toygun Dagdevir and Feridun Yavas: Department of Mechanical Engineering, The Faculty of Engineering of Erciyes University, Melikgazi, Kayseri 38039, Turkey
Yahya Erkan Akansu: Department of Mechanical Engineering, The Faculty of Engineering of Nigde University, Nigde 51200, Turkey
Ferhat Daldaban: Department of Electric & Electronic Engineering, The Faculty of Engineering Erciyes University Melikgazi,Kayseri 38039, Turkey




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